JPS62278159A - Manufacture of cadmium sulfide sintered membrane - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Application) The present invention provides a method for applying a paste containing cadmium sulfide (hereinafter referred to as CdS), cadmium chloride (hereinafter referred to as CdCβ2), and an organic vehicle onto an insulating substrate. The present invention relates to a method for producing a CdS sintered film obtained by coating, drying, and firing, particularly a CdS sintered film with a low resistance and large grain size intended for application to solar cells.

(Prior Art) CdS is an industrially useful material that is often used in photoconductive elements, photovoltaic elements, and the like. Recently, it has also been seen as promising as a window material for heterojunction solar cells.

Methods for manufacturing CdS films include evaporation, spraying, and vapor phase growth, but a manufacturing method with good yield and mass production is screen printing followed by sintering. In order to apply the CdS sintered film produced by this method to solar cells, it is required to have low electrical resistance.

Conventionally, CdS sintered films are manufactured by printing the above paste on an insulating substrate using a screen printer, etc., drying it, placing it in a boat with a perforated lid, and then heating and baking it at a constant temperature in an atmospheric furnace. (Japanese Patent Application Laid-Open No. 52-25305).

(Problems to be Solved by the Invention) The characteristics of this method are that the atmospheric gas can appropriately contact the membrane through the hole in the lid, and that it acts as a flux < CdCβ2
The amount of volatilization can be controlled to some extent by the size of the pores and the speed of temperature rise.

However, in this method, CdCJ2 is heated in an atmosphere at a temperature 100℃ higher than its melting point (568℃).
Cj! The situation is such that the two steams do not act sufficiently during sintering and are dissipated.

Therefore, it has not been possible to produce a CdS sintered film with large particle size, denseness, and low electrical resistance.

An object of the present invention is to stably supply a CdS sintered film that simultaneously satisfies grain growth and low electrical resistance, which have been difficult to produce using conventional methods.

(Means for solving gaps according to the invention) According to the present invention, a method for manufacturing a cadmium sulfide film by applying a paste containing cadmium sulfide powder, cadmium chloride, and an organic vehicle onto a substrate, drying it, and then subjecting it to heat treatment. In the heat treatment, oxygen is reduced to 0.
Melting of cadmium chloride in an atmosphere containing 1 to 20 vol%; Grain growth step in which cadmium sulfide is grown as grains by maintaining it at a temperature below its volatilization temperature in terms of H content; and a grain growth process in which it is maintained at a temperature above its volatilization temperature in a non-oxidizing atmosphere. ,
The above object is achieved by a method for producing a sintered cadmium sulfide film, which comprises a volatilization step of volatilizing cadmium chloride.

It is preferable to carry out the grain growth step at 530 to 600°C, or to carry out the volatilization step at 620 to 700°C, respectively.

The basic idea of the present invention will be briefly described below.

The present inventors carried out the contents described in the specification of JP-A No. 52-25305 as one of the methods to study methods for promoting grain growth of CdS. As a result, it was found that if the area of the holes made in 1M was reduced, grain growth progressed to some extent, but the grain size was large and a dense film could not be obtained.

However, it was possible to obtain a CdS film with a large particle size for the first time when using a non-porous lid, which had previously been pointed out to be inappropriate.

However, in this case, the electrical resistance of the membrane is several + to several hundred Ω.
/It reached the mouth, and the electrical resistance could not be lowered.

So the inventors.

CdCj! is the reason why the electrical resistance does not decrease! It was thought that this was because 2 remained at grain boundaries and on the film surface.

After that, in order to produce a sintered film that satisfies grain growth and low electrical resistance at the same time, the film placed in the firing container must be heated using CdCj! CdCj, which is no longer needed, is held for a certain period of time at a temperature where the liquid phase of 2 is formed, and then the temperature is raised. It was found that 2 could be removed through degassing, leading to the completion of the present invention.

(Preferred mode of implementation) The following steps (a) to () until the CdS sintered film is completed
d) and CdT on the CdS film produced through the above steps.
The process of forming an e-film and an ohmic electrode to form a solar cell (e
) and (f) will be explained in detail.

(a) Adjustment of CdS paste The CdS paste here refers to CdS powder.

Cd1l! , refers to a homogeneous mixture of vehicle and vehicle. The average particle size of the CdS powder contained in the paste is 0.1 to 10 μm. If it is less than 0.1 μm, the crystals will become large even if the grains grow. Conversely, if it exceeds 10 μm, the crystals will become large when applied to the substrate. 1. The surface is uneven, making it difficult to obtain a homogeneous film.

Cd(j may be in a powder state with a particle size similar to that of CdS, or may be dissolved in water, for example. However, the amount of CdCJ added is 5 to 20 wt% relative to CdS.
If it is less than 5% by weight, the film will have insufficient grain growth, and if it exceeds 20% by weight, it will remain in the film after sintering or the substrate glass will devitrify, which is not preferable.

The organic vehicle is an auxiliary agent that is mixed with the powder to improve workability in the subsequent coating process. Therefore, any viscous organic substance may be used, but it is preferable to use one with a boiling point as low as possible. Specifically, propylene glycol, ethylene glycol, etc. may be used.

The three components are thoroughly mixed using a mixer such as a three-roller to form a sticky paste.

(b) Application of CdS paste The paste prepared in (a) is printed on an insulating substrate to a desired size and thickness using, for example, a screen printer. The insulating substrate herein refers to, for example, an A1203 substrate, a borosilicate glass substrate, and the like. When considering application to solar cells, it is appropriate to use a glass substrate.

The coating method on the insulating substrate may be performed by using not only a screen printer but also a spray gun or a brush.

At this time, the coating film is controlled so that the film thickness after drying is approximately 10 to 100 μm. This is because if the film is thinner than 10 μm, it is difficult to achieve low electrical resistance, and if it exceeds 100 μm, cracks are likely to occur during sintering.

(c) Drying Drying is a process of removing organic substances from the paste applied on the insulating substrate. Therefore, this step may be performed in an atmospheric atmosphere. The drying temperature varies depending on the organic substance used, but is generally near the boiling point.

It is preferable to set the drying time to 60 to 30 minutes. If the drying time is shorter than this, organic substances tend to remain in the film, and if the drying time is made longer, energy is wasted.

(d) Firing Firing the CdS film is a central part of the present invention.

First stage (CdS grain growth step): CdS is dissolved and recrystallized in the molten CdCβ2 while being held at the temperature at the first stage entrance, and grain growth progresses.

The temperature at this time is preferably 530 to 600°C, and the atmosphere is preferably an atmosphere containing an inert gas and 0.1 to 20 vol % oxygen.

The holding time is approximately 1 to 2 hours to sufficiently dissolve CdS in the molten CdCl2. At this time, if the temperature in the 9-grain growth step is less than 530°C, CdC(2) will not melt, and if it exceeds 600°C, CdC112 will dissipate, which is not preferable.

At this time, if the firing atmosphere is only an inert gas, the following ■～■
Since the reaction shown in (a) does not occur, the composition does not become Cd-rich and the electrical resistance becomes high.

Cd S + 20 -Cd S O4...■C
dS+Cd50 →2Cd+2SO2↑・・・■z
Cd + (+-x)Cd S→Cd S l-x
-...■ Conversely, an atmosphere containing more than 20 vol % of oxygen is not preferable because CdS will be oxidized.

Those kept under the above conditions for at least 1 hour.

Crystal grains are 2 to 3 times larger than conventional ones. At this time, it is preferable to carry out the first stage treatment until the crystal grain size of CdS reaches approximately 25 μm or more. When the CdS grain growth is insufficient, the conversion efficiency tends to decrease correspondingly because light is scattered at grain boundaries of small crystal grains and does not sufficiently reach the PN junction.

Second stage (cdCI!2 volatilization step): CdC112 that is no longer needed is removed from the film while being held at the second stage temperature. Therefore, the heating temperature of the second stage is set higher than that of the first stage. Specifically speaking, the heating temperature is 620
~700℃ is best.

At temperatures below 620°C, CdCl2 tends to remain in the film.70
If the temperature exceeds 0° C., sublimation of CdS may occur or the glass substrate may become softened, which is not preferable.

The holding time for volatilization varies depending on the set temperature, but approximately 1 to 2 hours is appropriate. When CdCf2 remains between CdS crystal particles, the electrical resistance of the CdS film increases, and for example, if it exceeds 100 Ω/hole, the intrinsic conversion efficiency of the battery decreases to 5.
% or less, which is not preferable. Therefore, in this volatilization step, conditions are selected so that substantially no CdCf2 remains.

The atmosphere at this time is a non-oxidizing atmosphere to prevent oxidation of CdS.

Note that (e) CdTe film formation and (f) ohmic electrode formation are performed on the CdS film produced through the steps (a) to (d) to form a solar cell, but the following steps (e) and ( f) relates to an application example using the present invention as a basis.

Hereinafter, explanation will be made using a cross-sectional view of a solar cell illustrated in FIG. 1.

(e) Preparation of CdTe film Similar to the CdS film, the CdTe film is obtained by printing and baking a paste. However, the particle size of the CdTe powder in the paste is adjusted to ensure uniform contact between the CdTe scraper and the CdS film.
It is necessary to make the grain size smaller than that of CdS. Specifically, 01 to 1 μm is suitable.

The CdTe paste is obtained by mixing and kneading the CdTe powder with an appropriate amount of an organic vehicle (CdCJ) that acts as a flux.
5 to 5vt% is good; below this, the adhesive strength between CdS and CdTe will be weak, and if it exceeds 5vt96, CdCJ
! This is not preferable because 2 tends to remain and deteriorates battery performance.

The amount of organic vehicle is adjusted so that the paste has a viscosity that is easy to print. This paste is fired to a film thickness of 5 to 20 μm.
Print on the CdS film so that If the CdTe film is thinner than this, the CdTe electrode and the CdS film tend to become electrically conductive through the micropores of the film, making it impossible to operate as a battery. Conversely, if the CdTe film becomes thicker, the electrical resistance in the thickness direction (direction of current flow) increases, which is undesirable because it increases the internal resistance of the battery.

The printed CdTe film is dried and then fired under the same conditions as the CdS film. CdTe firing container.

The same material used for forming a CdS film may be used. However, the atmosphere should be non-oxidizing. Firing the CdTe film.

The CdTe film adheres to the CdS film with moderate strength, and the Cd
Temperature at which a diffusion layer is formed at the interface with the S film.

Do it in time. Specifically, firing may be performed at a temperature of 600 to 700°C for 1 to 2 hours. At lower temperatures and for a shorter time than this range, the adhesive strength between the CdTe film and the CdS film is weak, and at high temperatures,
A long time is not preferable because a thick CdTe S layer is formed at the bonding interface, which lowers the sensitivity -x x on the short wavelength side.

(f) 50 to 500 ppff on the CdTe film obtained in electrode formation (e)
After printing a carbon paste containing 1 of Cu, a predetermined f
An ohmic electrode is formed by firing in an inert gas containing f1 (preferably 0.5 to 5 vol%) oxygen at 300 to 500°C for 30 to 60 minutes. At this time C
u acts as an acceptor for the CdTe film.

Therefore, with carbon paste without Cu addition, only a battery with a low open circuit voltage (battery voltage in a state where no current is applied) can be obtained. However, if the amount of Cu added exceeds the above range, it is not preferable because Cu increases the resistance of the CdS film.

In addition, even if the carbon paste contains Cu, if the oxygen concentration in the firing atmosphere is lower than the above range, +Cd
It is difficult to form an ohmic electrode for the Te film, and conversely, if it is more than this, the electrical resistance of the carbon electrode increases, which is not preferable.

After this, Ag containing In was used as the ohmic electrode of the CdS film.
Bake the paste after printing.

The amount of In added may be 10 to 30 vt% based on the Ag paste. This is because if the amount is less than this, it is difficult to obtain ohmic contact, but even if more than this is added, the effect will hardly change. The above range is preferable from the point of view of reducing the amount of expensive In added.

The melting point of this Ag-In paste (15
It is possible to form an ohmic electrode for a CdS film by simply heating it for 30 to 60 minutes at a temperature 30 to 50°C higher than 6°C.

Finally, Ag paste is printed on the carbon strip and dried (
An auxiliary electrode is formed by allowing the solution to cool (at room temperature).

Example Next, CdS sintered film manufacturing method of the present invention was produced.
Examples 1 to 4 of dS sintered films and Example 5 of a solar cell using the CdS sintered films will be shown. Also, as a comparative example.

When the temperature of the CdS grain growth step is less than 530°C...Comparative example ICd (1
! When the atmosphere in the volatilization step in step 2 is an oxidizing atmosphere ...Comparative example 2 When the temperature is raised at a constant rate ...Comparative example 3 A solar cell and a CdS sintered film manufactured under the conditions of comparative example 3 were used. In the case where ... Comparative Example 4 is shown.

The CdS sintered film was evaluated based on the sheet resistance and average grain size (M) of the CdS sintered film.

In addition, evaluation of the solar cell was performed in the following manner.

Solar cell current under simulated sunlight with constant light intensity (
1) - Obtain voltage (V) characteristics by combining a potentiostat, a function generator, and an XY recorder.

That is, the voltage applied by a potentiostat in a direction that cancels out the battery voltage generated during light irradiation and the current flowing in the battery at that time are recorded on an X-Y plotter. If the applied voltage at this time is swept at a constant speed by a function generator, an IV curve as shown in FIG. 2 will be obtained.

From this curve, the combination (1.V) that gives the maximum output (
I , V ) (see Figure 2).

IIax l1ax The conversion efficiency was determined by the following formula.

P: Intensity of incident light S: Effective light receiving area (junction area) Example 1 73.94 parts by weight of CdS powder (purity 5N) with an average particle size of 2 μm, cdC12 powder (purity 4N) with an average particle size of 2 pm 1
0.08 parts by weight and 15.9 parts by weight of propylene'glycol
A CdS paste was prepared by thoroughly kneading 8 parts by weight. The paste was coated with borosilicate glass (10
It was printed to a size of 8 x 10 am on a paper (X 12 Xo, 8 mm). After leaving this at room temperature for 30 minutes and leveling.

! The propylene glycol was removed from the membrane by heating for 30 minutes in a drying oven set at 150°C. After that, a boat with a perforated lid (boat: 2
8 X 54 XQ, 5m+s, lid: 28X54X3a
+m, total hole area: 10mm, material: A, e 203)
The atmospheric gas (N2 containing 1vol9602) is 2f!
The sample was placed in an electric furnace flowing at a rate of 15° C./ff1 inch, and the temperature inside the furnace was raised at a rate of 15° C./ff1 inch to reach the temperature of the first stage. After the first stage was heated at H degrees for 1.5 hours to cause grain growth of CdS, the atmosphere was changed to N2 gas only, and the temperature inside the furnace was further increased to reach the second stage temperature.

By holding the temperature at the second stage for 1.5 hours, unnecessary CdCl2 was removed from the inside of the film.

Thereafter, the temperature inside the furnace was slowly cooled to room temperature to obtain a CdS sintered film.

Table 1 summarizes the relationship between the sheet resistance and average grain size of the CdS film obtained at this time and the temperatures of the first and second stages.

Table 1 Resistance: Sheet resistance Particle size: Average particle size Example 2 After printing and drying the CdS paste in the same manner as in Example 1, it was placed in a firing container and the crystallinity of the first stage (l) Q, 5v
N containing ol%0, 2J/ll1in) at 2
Time, second stage temperature (N, 2j!/m1n)
A CdS sintered film was prepared by heating for 1 hour. Table 2 summarizes the relationship between the sheet resistance and average grain size of the CdS film obtained at this time and the temperatures of the first and second stages.

Example 3 CdS paste (15vt% C
After printing and drying dC (containing 2).

Place in a firing container and heat at the temperature of the first stage (N containing 5 vol% 02, 2 J/aln) for 1 hour and at the temperature of the second stage (N, 2 J2/akin) for 2 hours.
A dS film was prepared. Table 3 summarizes the relationship between the sheet resistance and average grain size of the CdS film obtained at this time and the temperatures of the first and second stages.

Example 4 The CdS paste used in Example 1 was printed on a 110 x 110 borosilicate glass to a size of 100 x 100 mta, dried, and then printed on a boat with a perforated lid (boat: 115 x 115 x 8.5 mm, Lid: 115X115
X2mm, total area of holes 287II1112. Material: A (203), first heated at 560°C (N containing lvol% 0, 2J/1n) for 1.5 hours, then further heated at 670°C (
N, 2j! /5in) for 1.5 hours at C
A dS sintered film was produced.

In order to examine the uniformity of the films obtained in this manner, films having an area of 20 x 20 mm were cut out from the substrate, electrodes were attached, and the sheet resistance of each film was measured. As a result, as shown in Table 4, it was found that the electrical resistance value of the film had little variation from place to place, and the film was homogeneous even over a large area.

Table 4 Example 5 First stage of Example 1 560'CX 1.5 hours (lv
N, 2 j! containing ol%0! /1n) r second
Stage 690℃ x 1.5 hours (N, 2j!/5i
CdS film (size 8N10mm) fired under the conditions of n)
On top, a CdTe paste made by adding 1 wt% and 15 vt% of CdCJ and propylene glycol to CdTe powder (5N) crushed to 350 mesh under, respectively, was printed, dried, and then placed in an N2 atmosphere (2j!/alin
CdTe@ was formed by firing at 635 °C for 1.5 h in N2) (size 8N6 mm),
The CdS/CdTe solar cell is made by adding a carbon electrode (100 ppm of Cu) onto this CdTe film.
An Ag auxiliary electrode (Ag paste (DuPont 4929)) was placed on the CdS film. ) was heated in air at 180°C for 30 minutes).

The device obtained in this way is 100111w/CII
When placed under +2 solar simulator light (simulated sunlight), the intrinsic conversion efficiency was measured to be 9.0%.

Comparative Example 1 The same CdS paste as in Example 1 was heated at 450°C x 1 in the first stage.
．． 5 hours (N2゜2 J/l1in including lvol%O
), 2nd stage 670@CX1.5, time (N,
2j! /a+in) conditions. The sheet resistance of the obtained CdS film was 900 Ω/hole, and the average particle size was 1.
It was 5 μm.

Comparative Example 2 The same CdS paste as in Example 1 was heated at the first stage at 560°C x 1
．． 5 hours (N2゜2 including lvol%0, e/ff
1in), second stage 720℃ x 1 hour (1vol%
N including O, 2j! /a+in) conditions. The sheet resistance of the obtained CdS film was 800Ω/mouth,
The average particle size was 32 μm.

Comparative Example 3 A CdS paste was printed and dried on a borosilicate glass substrate in the same manner as in Example 1, and then placed in a firing container and heated in an electric furnace.

However, the firing conditions at this time were such that the temperature was increased from chamber 1 to 670°C at a rate of 10°C/Φin, held at 670°C for 1.5 hours, and then slowly cooled to around room temperature. What is the firing atmosphere?

N2 containing 1 vol% O was flowed from room temperature to 560°C, and only N2 was used at 560°C or higher and during slow cooling.

The sheet resistance of the CdS film obtained by this method was 1 Ω/hole, and the average particle size was 12 μm.

Comparative Example 4 A CdTe film, a carbon electrode, and an Ag-In electrode were formed on a CdS film fired under the conditions of Comparative Example 3 in the same manner as in Example 5 to produce a solar cell. Intrinsic conversion efficiency of a battery (yo3
%Met.

(Operations and Effects of the Invention) The CdS sintered film manufacturing method of the present invention maintains for a certain period of time at a temperature at which CdCl2 added as a flux becomes a melt, and after sufficient grain growth of CdS, unnecessary CdCf2 is volatilized. It is characterized by

The chemical action that allows the production method of the present invention to produce a CdS sintered film with a particle size 2 to 4 times larger (20 to 40 μm) than the conventional one (around 10 uffi) and an electrical resistance of about 1/10 or less (100 Ω/mouth or less). can be considered as follows.

During firing, a liquid phase of CdCl2 is formed, and since it is maintained at a temperature that is difficult to volatilize for a certain period of time, the CdCl necessary for grain growth is
2 melt is sufficiently retained within the membrane. CdS is dissolved in this melt and recrystallized to enlarge the particles. Furthermore, since the melt is uniformly distributed within the film, a CdS film with large grain size and homogeneity can be obtained.

However, as CdCl2 remains in the film as it is, it is not possible to bring out the original electrical properties of CdS, which has been made into a semiconductor due to reaction with oxygen. Therefore, by further increasing the temperature and removing Cd(, e2) from the film, lower electrical resistance can be achieved at the same time.

According to the method, the entire coating-drying-baking process can be automated. Moreover, since the resulting film has a large particle size and low electrical resistance, transparent electrodes (such as ITO films) conventionally used in solar cells are no longer necessary, making it possible to significantly reduce the cost of solar cells.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a cross section of a solar cell manufactured as an applied example of the present invention. FIG. 2 is a graph showing an IV curve showing an example of current (1)-voltage (V) characteristics of a solar cell. Patent applicant: Toyota Central Research Institute Co., Ltd.
Person, Patent Attorney Asamichi Kato (and 1 other person)

Claims (3)

[Claims] (1) A method of manufacturing a cadmium sulfide film by applying a paste containing cadmium sulfide powder, cadmium chloride, and an organic vehicle onto a substrate, drying it, and then subjecting it to a heat treatment, in which the heat treatment is performed using oxygen at 0.1 to 20V.
A grain growth step in which cadmium sulfide is grown by holding it at a temperature higher than the melting temperature of cadmium chloride and lower than its volatilization temperature in an atmosphere containing 0.1% of cadmium chloride. A method for producing a sintered cadmium sulfide film, comprising a volatilization step. (2) Claim No. 1, characterized in that the grain growth step is carried out within a temperature range of 530 to 600°C.
) A method for producing a cadmium sulfide sintered film as described in item 2. (3) Claim (1) characterized in that the volatilization step is carried out within a temperature range of 620 to 700°C.
The method for producing a cadmium sulfide sintered film according to item (2) or item (2).